For decades veterinarians have relied upon a number of different imaging tools, from radiographs to ultrasonography, to diagnose lameness, pregnancy, and soft-tissue-related conditions. In recent years a host of advanced imaging modalities such as digital radiography, CT, scintigraphy, and MRI have been added to the mix, bringing with them the ability to pinpoint lameness problems more accurately than ever.

Up until the 1970s, radiography (X rays) was the only imaging technique adapted for equine medicine. It was around that time the medical community started modifying other machines for horses in order to perform nuclear scintigraphy (bone scans, used to identify abnormalities in the bone and soft tissue) and computerized tomography scanning (CT, practical for examining feet, heads, and dental problems). Diagnostic ultrasonography came along in 1979, simplifying pregnancy diagnosis and the assessment of soft tissues--especially tendons and ligaments that could not be assessed via radiography.

It's even being used for guided injections, notes Kent Allen, DVM, owner of Virginia Equine Imaging in Middleburg, Va. Allen says it can be difficult to place medication or diagnostic anesthetic into some joints via injections, particularly the more difficult joints such as elbows, shoulders, hips, and the cervical spine or sacroiliac. The gold standard for injections is anatomical landmarks, but in some of these difficult joints, ultrasound can help. "When we are in the treatment phase, we can watch the needle go into the joint, penetrate the joint capsule, and watch your medication go in," says Allen.

Radiography systems have also improved with time, most significantly with the introduction of digital radiography. One of the biggest benefits to this technology is that images are of higher resolution, and they can be shared easily among veterinarians and their clients via CD or e-mail.

"Now, also, all of this information is stored digitally, where before we had these huge racks of X ray film and ultrasounds, and you would rummage through them and send someone up to the archives to look for them for half an hour," Allen recalls. "Nowadays, you go to a patient's file and you request to see the images, and all of the images are lined up, and you just pick what you want to see to compare the old ones to the new ones. It's tremendously more effective than it ever was before."

This has, however, created challenges for vets who are scrambling to update their information technology infrastructures. "A lot of veterinarians are still struggling with how to archive it, how to recall it, and how to store it for safety," Allen says. "We've depended upon paper and film archives, and now we've got to have a digital archive. It not only has to be in separate storage off of the main system, you've got to have all of these firewalls and protection, as well as fast Internet access so that you can move these files around."

Off-site storage facilities are necessary in case the files at the office are damaged. "Veterinarians who have purchased digital systems are starting to accumulate a lot of images, and they are now starting to come to terms with the storage aspect of it," says Allen.

MRI

The most groundbreaking new imaging development, however, has been the adaptation of MRI. Norm Rantanen, DVM, MS, Dipl. ACVR (radiology), a veterinary radiologist and an equine imaging consultant based in Fallbrook, Calif., explains that MRI allows a view inside the horse's foot and other areas small enough to fit within the confines of MRI unit. "We could X ray and do CT and scintigraphy of the foot, but we couldn't do any definitive imaging of the soft tissues in the foot; MRI has allowed us to do that," he explains, adding that MRI provides soft tissue definition better than CT in most instances.

For CT and standard MRI scanning, horses must be anesthetized; however, standing MRI units require only that the animal be tranquilized. The lower parts of the extremity can effectively be imaged in the standing horse.

One of the problems with imaging equipment such as CT and MRI is size of the patient: horses are big and the systems--designed for humans--are too small for total body imaging. This limits imaging procedures to the distal limb up through the carpus, hock, and even the stifle in some cases (although imaging the stifle can be very difficult). The head and neck can be imaged in smaller horses and foals.

"The limitations of all imaging modalities are: what can you see?" says Betsy Charles, DVM, of The Imaging Center at San Dieguito Equine Group (formerly Equest Diagnostic Imaging Center) in San Marcos, Calif. "MRI has limitations because we can only fit so much of the horse in the magnet. Most of the (stationary) MRI units in practice cannot accommodate the stifle, so this area is not yet routinely imaged."

Nuclear scintigraphy requires the handling of radioactive isotopes, which mandates the veterinarian be qualified to do so, and the facility must have a designated space to keep the horses when they are radioactive. Rantanen notes that scintigraphy is not super-specific. "It will tell you where a problem is in the body, but it doesn't have the resolution to tell you exactly what it is," he says. "If you use scintigraphy, it's usually followed by X ray, or sometimes MRI, or sometimes CT to figure out exactly what the problem is inside the structures."

Cost is a big issue with all of the modalities, with MRI being the most expensive. Horse owners can expect to pay upwards of $2,000 for the procedure, so you want to make sure you get a good image of the exact area of interest.

Standing MRI units are limited in how much the image is able to capture due a small field size and motion of the upper limb. "It's not something where you can survey up and down the limbs because it takes a long time to acquire the images," Rantanen explains, adding that stationary MRI machines can't be used to conduct sweeping surveys either. "If you are going to anesthetize a horse and do MRI, you want to make sure that you are looking at the place where the problem is. It's expensive, it requires anesthesia to look at multiple joints, so it's better to have all of your facts in hand."

Portable Imaging

Several of the modalities are available in portable format--such as radiography and ultrasound--eliminating the necessity of transporting the horse to a centralized hospital. Rantanen points out that the advancements made in miniature electronics have reduced the quality differences between portable and stationary technologies.

"They are taking some of the mainframe ultrasound platforms and shrinking them down to notebook-sized computers," he says. "A lot of them have all of the special functions that the big systems have, including Doppler flow studies for cardiac and vascular work, and high frequency and multiple frequency scanheads."

Portable radiography is available as both conventional radiography (wet-film) and using digital technologies such as computed and digital radiography. All can provide diagnostic images, but digital technologies allow easy image sharing and storage.

The Lame Horse

After clinical exam and diagnostic blocking, radiography and ultrasound remain the diagnostic tools used most often in diagnosing lameness, as they are relatively inexpensive, noninvasive, and provide good information. However, they might not give the veterinarian a final answer about what is causing the lameness. How the veterinarian proceeds from there depends on the injury and, of course, the horse owner's limitations.

At The Imaging Center, veterinarians have access to a standing MRI unit, nuclear scintigraphy, digital radiography, and ultrasound. The facility does not currently have a CT system on site, but there is one in the area that they can use.

"Until recently, we have been dependent on radiography and ultrasound when dealing with foot lameness," says Charles. "These modalities provide good information, but it may not be enough. Now we have another step we can take. We use a combination of MRI and scintigraphy--in addition to diagnostic blocks, radiology, and ultrasound--to try to figure out what's going on in horses' feet. This has really helped us more accurately identify what is going on in the foot. MRI has given us a whole new window into the soft tissue and bony structures of the foot."

Rantanen declares that MRI has enabled the veterinary community to do a better job of evaluating lame horses. "MRI is a very specific examination: you do it on a specific joint or a specific area," he says. "We make better use of our clinical skills and our regional anesthesia skills. We may get our answer using some of the less expensive modalities, and we may not have to use MRI, but if we get to that point where we have done everything, and we know it's in the foot, and it doesn't show on X ray, and we can't ultrasound through a hoof wall, then we will use the MRI."

One area where this has proven revolutionary is in the diagnosis of navicular area problems, which usually cannot be ruled out using X rays. "The MRI has allowed us to be very definitive," Rantanen explains. "We are also able to look at the other structures in the foot. It's not unusual for a navicular bone problem to be associated with a tendon or other problem as well. It's impossible to find that with an X ray because you can't adequately see those soft tissues within the hoof capsule."

When the navicular bone is injured, MRI helps us monitor the changes in the injury and the progress in recovery. "It used to be that once you made a clinical diagnosis of so-called navicular disease in horses, it was the end of the world," says Rantanen. "We are finding now that some navicular injuries will resolve with time and treatment."

Take-Home Message

The available array of imaging tools adds to the veterinarian's ability to diagnose and treat a variety of diseases, injuries, and lamenesses. As technology improves, these tools are becoming more mobile, and veterinarians are able to take the imaging equipment to the horse in the field.

About the Author

Carolyn Heinze (carolynheinze.blogspot.com) is a freelance writer/editor. She currently works from her pied à terre in Paris, France, where she continually dreams of convincing the French Republican Guard to let her have a go-round on one of its magnificent horses. One can dream, can't they?

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